Abstract: Trichoderma harzianum SH2303 with high biocontrol activity against southern corn leaf blight (SCLB) was isolated from field soil. Pretreated detached maize leaves with T. harzianum SH2303 showed induced resistance to SCLB with a duration of 15 days. Efficacy of T. harzianum SH2303 against SCLB reached 78.1% and 56.3% under greenhouse and field conditions respectively when spraying spore suspension over maize seedling leaves prior to inoculation of the pathogen. The activities of phenylalanine ammonia lyase (PAL) and superoxide dismutase (SOD) in maize leaves peaked at 36 h in the Trichoderma treatments after pathogen challenging inoculation. RNA expression levels of Pal and Sod were also upregulated in pace with the enzyme activity. Results indicated that induced resistance might be one of the important mechanisms in the biocontrol of SCLB by T. harzianum SH2303.